Newbie having trouble with beatsin8 on longer LED Strip

Hi,

Very new to FastLED so I'm sure the issue I'm having is a simple thing I've overlooked, but I have done some research and have struggled to solve the problem. I am following this tutorial, and with the first function he tries, my strip, instead of a smooth sine wave going back and forth across my strip, breaks frequently and won't stay connected.

My strip is 144 leds long but if I'm correct, that should still be in the correct range for the 8 bit integer values. I've tried slowing the frequency down, and even near 1 bpm, the wave still skips every 2 or 3 leds, especially near the middle. I've noticed if I lower the value of NUM_LEDS to anything below 83, the wave no longer skips, and if I change my beatsin8 to beatsin16, there is less skipping, but it's definitely still there. Anyways like I said I'm sure I'm overlooking something simple, but I'm very new to FastLED so any help is appreciated. Here is a link to my code.